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Canon XF Series HD Camcorders
Canon XF305, XF205 and XF105 (with SDI), Canon XF300, XF200 and XF100 (without SDI).


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Old January 24th, 2011, 10:06 AM   #1
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Base ISO of XF100

Hi:

Whenever I see light sensitivity for video cameras the specify minimum lux, but I find that pretty much useless, first I have no feeling with how much a lux is, but worse, it doesn't say what kind of image can be obtained with that light.

In DSLR photography a base ISO is given for the sensor, any other ISO is obtained adjusting the gain. This is great because I can take any camera out set ISO and aperture in a setting I know and control and compare.

So, what is the base ISO of the XF100 sensor at 1080p?

Thanks, Erik
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Old January 24th, 2011, 12:21 PM   #2
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Eric, not to niggle but... I have an XF-300 and 1D Mark IV, I've shot decent-looking video on the Mark IV at ISO 2000 and higher (club stuff, out of necessity). That's well above what might be considered a "base ISO" of (I think) 100 for that camera.

When you take into account improvements in signal processing and low-noise amplification, internal noise reduction (software algorithms), etc. I don't think a 'base ISO' is a really useful indicator. It leaves too much out that can affect the video. IMO and YMMV.

cheers

Brett
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Old January 24th, 2011, 02:03 PM   #3
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Thanks for your reply, but the thing is, the base ISO gives the best image quality, the more gain the more noise, that's not to say that boosting the ISO cannot produce usable footage, I know that 3dB gain doubles the ISO, but I have no reference point to start from.

The problem I have with the specifications is that they write minimum sensitivity in lux, which does not say anything about the image quality you get at that lighting. This means I can't compare two cameras or get any reasonable expectation of lowlight performance.

Knowing the base ISO, I can compare cameras and I can use a light meter to see if there is enough light in any given situation, how much gain might be needed etc. Of course, there are more things to image quality, in particular once gain is used how is noise reduction. But the base ISO together with max aperture give a good reference of lowlight performance.

If sensor technology was fixed, it would be fairly easy to calculate a base ISO from that of another known sensor: I hava Nikon with a full frame sensor 10Mpx with base ISO 200. The full frame sensor is 50 times the size of the 1/3" sensor of the Canon XF100, with about 5 times as many pixels. So, if sensitivity is pure geometry (pixels per mm2), that means the XF100 sensor should have a base ISO 20. I believe it to be better as my Nikon is two years old, but is it ISO 25, 50 or maybe even 100?
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Old January 24th, 2011, 04:37 PM   #4
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From memory of measurements I did early last year it is something under 100 ISO, I think 80 @ - 6 gain
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Old January 24th, 2011, 04:55 PM   #5
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nick-

thank u for the info.

how does iso80 work w/-6 gain?

if by adding gain to get to zero/0, wouldn't that increase the iso?

thanks

be well

rob
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Old January 24th, 2011, 05:12 PM   #6
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Can't help you on the numbers/specs question about base ISO but have you seen this XF100 test video? It's one of very few around at the moment - but at least it has some night footage that you can study to see how the camera handles the darker shots (with the gain settings he used).

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Old January 24th, 2011, 05:58 PM   #7
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andy-

thank you for sharing.

i have seen that footage when it was posted a month or so ago.

it is exactly the linked footage and the time lapse footage from these good folks at les films associes that has me interested in the canon xf100.

i am often in situations where low light is not a problem.

if decent glass, a good front-end chip (even if there is only one of these chips!), a 422 color space, dual xlr inputs and a worthy codec can be had in a stealth package for less than $3k, then i'll be at abel cine in new york to pick one up.

ymmv

be well

rob
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Old January 25th, 2011, 04:06 PM   #8
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Quote:
Originally Posted by Rob Katz View Post
nick-

thank u for the info.

how does iso80 work w/-6 gain?

if by adding gain to get to zero/0, wouldn't that increase the iso?

thanks

be well

rob
Hi Rob, I think it makes 0 gain 100 iso. It is a very small amount. I don't have a camera to hand and did not write settings down.

Again, from memory, the max usable gain (+18) equates to around 800 ISO. Not in the DSLR realms, but then there is the 5D MkII for that.
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